This invention relates to a screw grommet made of a plastic material which is used to bolt printed circuit boards and various other parts to an electric machine or apparatus, an automobile chassis or other bodies.
A variety of plastic screw grommets have been hitherto proposed. One screw grommet which is widely used is a headed article having an inserting leg and a collar-shaped head integrally connected to the inserting leg. The leg has a tapped longitudinal hole and raised portions on the outer surface thereof. In use the grommet is pushed into an aperture of a plate which constitutes a part of an electric machine or apparatus or an automobile chassis. The leg of the grommet is pushed in the aperture, yieldingly reducing the diameter of the raised portion of the leg in passing through the aperture and allowing the raised portion of the leg to return to its original shape and size at the under surface of the plate. The grommet is positively fixed to the plate by sandwiching the thickness of the plate in between the head of the grommet and the raised portion of the leg of the grommet. An object to be fixed is laid on the head of the grommet, and a bolt is inserted and screwed in an aperture of the object, the aperture of the head and the tapped hole of the leg of the grommet. The bolt when driven into the tapped hole of the leg of the grommet, will cause the leg of the grommet to enlarge in diameter, thus positively preventing the grommet from slipping out from the aperture of the plate.
As mentioned above, the grommet is fixed in an aperture of a plate by yieldingly reducing the diameter of the bulge portion of the leg as it passes through the aperture of the plate. The plate, however, is usually made of a metal, and therefore it is likely that the bulge portion of the leg will be cut off and removed by the circumferential edge of the aperture of the plate. Consequently, the bulge portion of the leg cannot be raised as much as required for positive anchoring with the undersurface of the plate. In some instances it is very difficult to insert the bulge portion of the leg into an aperture of a plate against the resistive friction between the leg and the edge of the aperture.
The object of this invention, therefore, is to provide a screw grommet which can be easily fitted in an aperture of a plate and can still assure positive engagement with the plate.